Cooling water scale and corrosion inhibition

ABSTRACT

A methods of the present invention for inhibiting silica scale formation and corrosion in aqueous systems where soluble silica residuals (SiO 2 ) are maintained in excess of 200 mg/L, and source water silica deposition is inhibited with silica accumulations as high as 4000 mg/L (cycled accumulation) from evaporation and concentration of source water. The methods of the present invention also provides inhibition of corrosion for carbon steel at corrosion rates of less than 0.3 mpy (mils per year), and less than 0.1 mpy for copper, copper alloy, and stainless steel alloys in highly concentrated (high dissolved solids) waters. The methods of the present invention comprise pretreatment removal of hardness ions from the makeup source water, maintenance of electrical conductivity, and elevating the pH level of the aqueous environment. Thereafter, specified water chemistry residual ranges are maintained in the aqueous system to achieve inhibition of scale and corrosion.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

Silica is one of the major scale and fouling problems in many processesusing water. Silica is difficult to deal with because it can assume manylow solubility chemical forms depending on the water chemistry and metalsurface temperature conditions. Below about pH 9.0, monomeric silica haslimited solubility (125-180 mg/L as SiO₂) and tends to polymerize asthese concentrations are exceeded to form insoluble (amorphous)oligomeric or colloidal silica. At higher pH, particularly above aboutpH 9.0, silica is soluble at increased concentrations of the monomericsilicate ion or in the multimeric forms of silica. Since conversion canbe slow, all of these forms may exist at any one time. The silicate ioncan react with polyvalent cations like magnesium and calcium commonlypresent in process waters to produce salts with very limited solubility.Thus it is common for a mixture of many forms to be present: monomeric,oligomeric and colloidal silica; magnesium silicate, calcium silicateand other silicate salts. In describing this complex system, it iscommon practice to refer to the mixture merely as silica or as silicaand silicate. Herein these terms are used interchangeably.

To address such problem, methods of the present inventions forcontrolling deposition and fouling of silica or silicate salts onsurfaces in a aqueous process have been derived and include: 1)inhibiting precipitation of the material from the process water; 2)dispersing precipitated material after it has formed in the bulk water;3) maintaining an aqueous chemical environment that supports formationof increased residuals of soluble silica species; and 4) producing anon-adherent form of silica precipitants in the bulk water. The exactmechanism by which specific scale inhibition methods of the presentinventions function is not well understood.

In industrial application, most scale and corrosion control methods ofthe present inventions used in aqueous systems typically rely on theaddition of a scale and corrosion inhibitor in combination withcontrolled wastage of system water to prevent scale and corrosionproblems. In this regard, the major scale formation potentials arecontributed by the quantity of hardness (calcium and magnesium) andsilica ions contributed by the source water, while the major corrosivepotential results from the ionic or electrolytic strength in the systemwater.

Treatment methods of the present inventions to minimize corrosion havefurther generally relied on the addition of chemical additives thatinhibit corrosion through suppression of corrosive reactions occurringat either the anode or the cathode present on the metal surface, orcombinations of chemical additives that inhibit reactions at both theanode and cathode. The most commonly applied anodic inhibitors includechromate, molybdate, orthophosphate, nitrite and silicate whereas themost commonly applied cathodic inhibitors include polyphosphate, zinc,organic phosphates and calcium carbonate.

In view of toxicity and environmental concerns, the use of highlyeffective heavy metal corrosion inhibitors, such as chromate, have beenstrictly prohibited and most methods of the present inventions now relyon a balance of the scale formation and corrosive tendencies of thesystem water and are referred to in the art as alkaline treatmentapproaches. This balance, as applied in such treatment approaches, isdefined by control of system water chemistry with indices such as LSI orRyznar, and is used in conjunction with combinations of scale andcorrosion inhibitor additives to inhibit scale formation and optimizecorrosion protection at maximum concentration of dissolved solids in thesource water. These methods of the present inventions, however, arestill limited by the maximum concentration of silica and potential forsilicate scale formation. Moreover, corrosion rates are alsosignificantly higher than those available with use of heavy metals suchas chromate. Along these lines, since the use of chromate and othertoxic heavy metals has been restricted, as discussed above, corrosionprotection has generally been limited to optimum ranges of 2 to 5 milsper year (mpy) for carbon steel when treating typical source waterqualities with current corrosion control methods of the presentinventions. Source waters that are high in dissolved solids or arenaturally soft are even more difficult to treat, and typically have evenhigher corrosion rates.

In an alternative approach, a significant number of methods of thepresent inventions for controlling scale rely on addition of acid totreated systems to control pH and reduce scaling potentials at higherconcentrations of source water chemistry. Such method allowsconservation of water through modification of the concentrated sourcewater, while maintaining balance of the scale formation and corrosivetendencies of the water. Despite such advantages, these methods of thepresent inventions have the drawback of being prone to greater risk ofscale and/or corrosion consequences with excursions with the acid/pHcontrol system. Moreover, there is an overall increase in corrosionpotential due to the higher ionic or electrolytic strength of the waterthat results from addition of acid ions that are concentrated along withions in the source water. Lower pH corrosion control methods of thepresent inventions further rely on significantly higher chemicaladditive residuals to offset corrosive tendencies, but are limited ineffectiveness without the use of heavy metals. Silica concentration muststill be controlled at maximum residuals by system water wastage toavoid potential silica scaling.

In a further approach, source water is pretreated to remove hardnessions in a small proportion of systems to control calcium and magnesiumscale potentials. These applications, however, have still relied oncontrol of silica residuals at previous maximum guideline levels throughwater wastage to prevent silica scale deposits. Corrosion protection isalso less effective with softened water due to elimination of thebalance of scale and corrosion tendency provided by the natural hardnessin the source water.

Accordingly, there is a substantial need in the art for methods of thepresent inventions that are efficiently operative to inhibit corrosionand scale formation that do not rely upon the use of heavy metals,extensive acidification and/or water wastage that are known andpracticed in the prior art. There is additionally a need in the art forsuch processes that, in addition to being efficient, are extremelycost-effective and environmentally safe. Exemplary of those processesthat would likely benefit from such methods of the present inventionswould include cooling water processes, cooling tower systems,evaporative coolers, cooling lakes or ponds, and closed or secondarycooling and heating loops. In each of these processes, heat istransferred to or from the water. In evaporative cooling waterprocesses, heat is added to the water and evaporation of some of thewater takes place. As the water is evaporated, the silica (or silicates)will concentrate and if the silica concentration exceeds its solubility,it can deposit to form either a vitreous coating or an adherent scalethat can normally be removed only by laborious mechanical or chemicalcleaning. Along these lines, at some point in the above processes, heatis extracted from the water, making any dissolved silicate less solubleand thus further likely to deposit on surfaces, thus requiring removal.Accordingly, a methods of the present invention for preventing foulingof surfaces with silica or silicates, that further allows the use ofhigher levels of silica/silicates for corrosion control would beexceptionally advantageous. In this respect for cooling water, aninhibition method has long been sought after that would enable silica tobe used as a non-toxic and environmentally friendly corrosion inhibitor.

To address these specific concerns, the current practice in theseparticular processes is to limit the silica or silicate concentration inthe water so that deposition from these compounds does not occur. Forexample in cooling water, the accepted practice is to limit the amountof silica or silicates to about 150 mg/L, expressed as SiO₂. Reportedly,the best technology currently available for control of silica orsilicates in cooling water is either various low molecular weightpolymers, various organic phosphate chemistries, and combinationsthereof. Even with use of these chemical additives, however, silica isstill limited to 180 mg/L in most system applications. Because in manyarid areas of the U.S. and other parts of the world make-up water maycontain from 50-90 mg/L silica, cooling water can only be concentrated 2to 3 times such levels before the risk of silica or silicate depositionbecomes too great. A method that would enable greater re-use or cyclingof this silica-limited cooling water would be a great benefit to theseareas.

SUMMARY OF THE INVENTION

The present invention specifically addresses and alleviates theabove-identified deficiencies in the art. In this regard, the inventionrelates to methods for controlling silica and silicate fouling problems,as well as corrosion of system metallurgy (i.e. metal substrates) inaqueous systems with high concentrations of dissolved solids. Moreparticularly, the invention is directed to the removal of hardness ionsfrom the source water and control of specified chemistry residuals inthe aqueous system to inhibit deposition of magnesium silicate and othersilicate and silica scales on system surfaces, and to inhibit corrosionof system metallurgy. To that end, we have unexpectedly discovered thatthe difficult silica and silicate scaling problems that occur in aqueoussystems when silica residuals exceed 200 mg/L as SiO₂ or reach as highas 4000 mg/L of silica accumulation (cycled accumulation from sourcewater) can be controlled by initially removing hardness ions (calciumand magnesium) from the makeup source water (i.e., water fed to theaqueous system) using pretreatment methods of the present inventionsknown in the art, such as through the use of ion exchange resins,selective ion removal with reverse osmosis, reverse osmosis,electrochemical removal, chemical precipitation, orevaporation/distillation. Preferably, the pretreatment methods of thepresent invention will maintain the total hardness in the makeup waterat less than 20% of the makeup silica residual (mg/L SiO₂), asdetermined from an initial assessment of the source water. In someembodiments, the total hardness ions will be maintained at less than 5%of the makeup silica residual. When source makeup water is naturallysoft, with less than 10 mg/L hardness as CaCO₃, pretreatment removal ofhardness ions may be bypassed in some systems. Thereafter, theconductivity (non-neutralized) in the aqueous system is controlled suchthat the same is maintained between 10,000 and 150,000 [mhos, andpreferably between 20,000 to 150,000 μmhos and the pH of the sourcewater elevated to a pH of 9.0, and preferably 9.6, or higher. Withrespect to the latter, the pH may be adjusted by the addition of analkaline agent, such as sodium hydroxide, or by simply removing aportion of the aqueous system water through such well known techniquesor processes as evaporation and/or distillation.

In a related application, we have unexpectedly discovered that theexcessive corrosion of carbon steel, copper, copper alloys, andstainless steel alloys in aqueous systems due to high ionic strength(electrolytic potential) contributed by high dissolved solids sourcewater or highly cycled (10,000 to 150,000 μmhos non-neutralizedconductivity) systems can likewise be controlled by the methods of thepresent inventions of the present invention. In such context, themethods of the present invention comprises removing hardness ions(calcium and magnesium) from the makeup source water using knownpretreatment methods of the present inventions, such as ion exchangeresins, selective ion removal with reverse osmosis, reverse osmosis,electrochemical removal, chemical precipitation, orevaporation/distillation. The pretreatment methods of the presentinvention will preferably maintain the total hardness ratio in themakeup water at less than 20%, and preferably at least less than 5%, ofthe makeup silica residual (mg/L SiO₂), as determined from an initialanalysis of the source water. When source makeup water is naturallysoft, with less than 10 mg/L hardness as CaCO₃, pretreatment removal ofhardness ions may be bypassed in some systems. Thereafter, theconductivity (non-neutralized) in the aqueous system is controlled suchthat the same is maintained between 10,000 and 150,000, and morepreferably 20,000 to 150,000, μmhos. Alkalinity is then controlled asquantified by pH at 9.0 or higher, with a pH of 9.6 being more highlydesired in some applications. Control of soluble silica at a minimumresidual concentration of 200 mg/L as SiO₂ to support corrosioninhibition. With respect to the latter, the SiO₂ may be adjusted by theaddition of a silica/silicate agent, such as sodium silicate, or bysimply removing a portion of the aqueous system water through such wellknown techniques or processes as evaporation and/or distillation.

DETAILED DESCRIPTION OF THE INVENTION

The detailed description set forth below is intended as a description ofthe presently preferred embodiment of the invention, and is not intendedto represent the only form in which the present invention may beconstructed or utilized. The description sets forth the functions andsequences of steps for constructing and operating the invention. It isto be understood, however, that the same or equivalent functions andsequences may be accomplished by different embodiments and that they arealso intended to be encompassed within the scope of the invention.

According to the present invention, there is disclosed methods forinhibiting silica and silicate scale in aqueous systems and providingexceptional metal corrosion protection that comprise the removal ofhardness from the makeup source water prior to being fed into theaqueous system and thereafter controlling the aqueous system withinspecified water chemistry control ranges. Specifically, hardness ions(calcium and magnesium) are removed from the makeup source water usingpretreatment methods known in the art, which include methods such as ionexchange resins, selective ion removal with reverse osmosis, reverseosmosis, electrochemical removal, chemical precipitation, orevaporation/distillation. The pretreatment methods will preferablymaintain the total hardness ratio in the makeup water at less than 20%of the makeup silica residual (mg/L SiO₂). In a more highly preferredembodiment, the pretreatment methods will maintain the total hardnessions present in the makeup water at less than 5% of the makeup silicaresidual. As will be appreciated by those skilled in the art, the silicaresidual can be readily determined by utilizing known techniques, andwill preferably be determined prior to the application of the methods ofthe present invention. Along these lines, when source makeup water isnaturally soft, with less than 10 mg/L hardness as CaCO₃, pretreatmentremoval of hardness ions may be bypassed in some systems.

Conductivity (non-neutralized) is controlled in the aqueous system suchthat the same is between approximately 10,000 and 150,000 μmhos throughcontrol or elimination of blowdown wastage from the system. In a morehighly preferred embodiment, conductivity will be maintained betweenapproximately 20,000 and 150,000 μmhos. The higher level of ionicstrength in this control range increases the solubility of multivalentmetal salts that are less soluble at lower ionic strengths of othermethods of the present inventions. This residual control parameter alsoprovides indirect control of silica and alkalinity (pH) residualscontributed by concentration of naturally available silica andalkalinity in the source water or by addition of adjunct forms of thesechemicals.

Aqueous system pH is maintained at 9.0 or greater as contributed by thecycled accumulation of alkalinity from the source water or throughsupplemental addition of an alkalinity adjunct, such as sodiumhydroxide, to the system when required. The minimum pH will provideincreased solubility of silica and control of silicate scale and supportcorrosion protection for metals. Along these lines, in certain preferredembodiments of the present invention, the pH may be raised andmaintained to a level of 9.6 of higher.

Silica residuals (soluble) will be maintained in the system at levels ofgreater than 200 mg/L as contributed by the cycled accumulation ofsilica from the source water or through supplemental addition of adjunctforms of silica to the system when required. In certain applications,such levels may be maintained at levels of greater than 300 mg/L. Theminimum residual of soluble silica will support corrosion inhibition formetals, and more particularly, inhibit corrosion of carbon steel to lessthan 0.3 mpy and less than 0.1 mpy for copper, copper alloys andstainless steel alloys present in the aqueous system.

With respect to the mechanisms by which the methods of the presentinventions effectively achieve their results, excess source water silica(beyond the soluble residuals attained with specified pH control) isprobably adsorbed as non-adherent precipitates that form followingreaction with small amounts of metals (Ca, Mg, Fe, Al, Zn) or solidsintroduced by source water or scrubbed from the air by the tower system.This is the probable result of the expanded solubility of the monomericand multimeric species of silica with the methods of the presentinvention that impede polymerization of excess silica until it reactswith these incrementally introduced adsorption materials to form smallquantities of non-adherent precipitants. The adsorption andprecipitation of high ratios of silica on small amounts of solids suchas magnesium hydroxide has been demonstrated by the Freundlichisotherms, and is common experience in water treatment chemicalprecipitation processes. The small quantity of precipitate is removedfrom the circulating water through settling in the tower basin or driftlosses.

Control of the lower solubility hardness scale formations and resultantnucleation sites on cooling system surfaces are controlled with themethods of the present invention disclosed herein, through pretreatmentremoval of the majority of the scale forming (hardness) metal ions andcontrol of system water at the specified higher ionic strength controlranges. The higher level of ionic strength in this control rangeincreases the solubility of scale forming metal salts. Such approach iswell suited to address a further complication in controlling silica andsilicate fouling brought about from the phenomena that colloidal silicatends to be more soluble as temperature is raised, while the polyvalentmetal salts of the silicate ion tend to be less soluble with increasingtemperature. As a result, control or minimization of polyvalent metalsin the aqueous solution will prohibit formation of the insoluble saltson heat transfer surfaces, and promote increased solubility of otherforms of silica at the elevated temperatures of heat transfer surfaces.The present methods thereby eliminate potential reaction of insolublesilica forms with hardness scale or metal salt deposits on systemsurfaces and their nucleation sites that initiate silica or silicatescale formations.

The higher residuals of soluble silica and higher pH levels maintainedvia the present methods of the present inventions provide highlyeffective polarization (corrosion barrier formation) and exceptionalcorrosion protection for carbon steel, copper, copper alloy andstainless steel metals (less than 0.3 mpy for mild steel, and less than0.1 mpy copper, copper alloy, and stainless steel). Comparable corrosionrates for carbon steel in aqueous systems with existing methods of thepresent inventions are optimally in the range of 2 to 5 mpy. Though notfully understood, several corrosion inhibition mechanisms are believedto be contributing to the metals corrosion protection provided by themethods of the present inventions of the present invention, and thesynergy of both anodic and cathodic inhibition functions may contributeto the corrosion inhibition process.

An anodic corrosion inhibitor mechanism results from increased residualsof soluble silica provided by the present methods, particularly in themultimeric form. Silicates inhibit aqueous corrosion by hydrolyzing toform negatively charged colloidal particles. These particles migrate toanodic sites and precipitate on the metal surfaces where they react withmetallic ion corrosion products. The result is the formation of aself-repairing gel whose growth is self-limited through inhibition offurther corrosion at the metal surface. Unlike the monomeric silica formnormally found in source water that fails to provide effective corrosioninhibition, the methods of the present invention provide such beneficialeffect by relying upon the presence and on control of total solublesilica residuals, with conversion of natural monomeric silica to themultimeric forms of silica at much higher levels, through application ofthe combined control ranges as set forth above. In this regard, theremoval of most source water calcium and magnesium ions is operative toprevent reaction and adsorption of the multimeric silica forms on themetal oxide or metal salt precipitates from source water, which isbelieved to be an important contribution to the effectiveness of thiscorrosion inhibition mechanism afforded by the present invention. Theresultant effective formation and control of the multimeric silicaresiduals with such methods of the present invention has not heretoforebeen available.

In addition to an anodic corrosion inhibition mechanism, a cathodicinhibition mechanism is also believed to be present. Such inhibition iscaused by an increased hydroxyl ion concentration provided with thehigher pH control range utilized in the practice of the presentinvention. In this regard, iron and steel are generally consideredpassive to corrosion in the pH range of 10 to 12. The elevated residualof hydroxyl ions supports equilibrium with hydroxyl ion produced duringoxygen reduction at the cathode, and increases hydroxyl ion availabilityto react with iron to form ferrous hydroxide. As a consequence, ferroushydroxide precipitates form at the metal surface due to very lowsolubility. The ferrous hydroxide will further oxidize to ferric oxide,but these iron reaction products remain insoluble at the higher pHlevels attained by implementing the methods described herein to polarizeor form a barrier that limits further corrosion. At the 9 to 10 pH range(as utilized in the practice of the present invention), effectivehydroxyl ion passivation of metal surfaces may be aided by thepretreatment reduction of hardness ions (calcium and magnesium) in thesource water that may compete with this reaction and interfere withmetal surface barrier formation.

Galvanized steel and aluminum may be protected in general by thesilicate corrosion inhibitor mechanism discussed herein, but protectivefilms may be destabilized at water-air-metal interfaces. Steel, copper,copper alloy, stainless steel, fiberglass, and plastic are thus idealaqueous system materials for application of the methods of the presentinventions of the present invention.

The extensive improvement in corrosion protection provided by themethods of the present invention is not normally attainable with priorart methods when they utilize significantly higher residuals ofaggressive ions (e.g., chloride and sulfate) and the accompanyinggreater ionic or electrolytic strength present in the aqueous systemwater. This may result from either use of acid for scale control and/orconcentration of source water ions in the aqueous system. As is known,corrosion rates generally increase proportionately with increasing ionicstrength. Accordingly, through the ability to protect system metalsexposed to this increased electrolytic corrosion potential, opportunityfor water conservation and environmental benefits that result withelimination of system discharge used with previous methods to reducecorrosion or scaling problems in aqueous systems can be readily realizedthrough the practice of the methods disclosed herein.

Still further, the methods of the present inventions of the presentinvention can advantageously provide gradual removal of hardness scaledeposits from metal surfaces. This benefit is accomplished through bothpretreatment removal of the majority of the scale forming (hardness)metal ions and control of system water at the specified higher ionicstrength control ranges. Solubility of hardness salts is increased bythe higher ionic strength (conductivity) provided by the present methodsof the present invention, which has been determined with high solidswater such as seawater, and may contribute to the increased solubilityof deposits present within the aqueous environment so treated. Studiesconducted with hardness scale coated metal coupons in treated systemsdemonstrated a significant deposit removal rate for CaCO₃ scale films inten days. Control of source water hardness at lower specified residualswill probably be required to achieve optimum rate of hardness scaleremoval.

Furthermore, the present methods advantageously prohibits microorganismpropagation due to the higher pH and dissolved solids levels that areattained. Biological fouling potentials are thus significantly reduced.In this regard, the methods of the present inventions disclosed hereincreate a chemical environment that inhibits many microbiological speciesthat propagate at the pH and dissolved solids chemistry ranges used withprevious treatment approaches. The reduction in aqueous system dischargealso permits use of residual biocides at more effective and economicaldosages that impede development of problem concentrations of anymicrobiological species that are resilient in the aqueous environmentgenerated through the practice of the methods of the present inventionsdisclosed herein.

A still further advantage of the methods of the present inventioninclude the ability of the same to provide a lower freeze temperature inthe aqueous system, comparable to ocean water, and avert potentialmechanical damage from freezing and/or operational restrictions forsystems located in freeze temperature climates.

Additional modifications and improvements of the present invention mayalso be apparent to those of ordinary skill in the art. Thus, theparticular combination of parts and steps described and illustratedherein is intended to represent only certain embodiments of the presentinvention, and is not intended to serve as limitations of alternativedevices and methods of the present inventions within the spirit andscope of the invention. For example, since the methods of the presentinvention provides both effective silicate scale control and corrosioninhibition when using high silica or high dissolved solids sourcewaters, extensive variation in source water quality can be tolerated.These source waters might otherwise be unacceptable and uneconomical foruse in such aqueous systems. In addition, such modifications mayinclude, for example, using other conventional water treatment chemicalsalong with the methods of the present invention, and could include otherscale inhibitors, such as for example phosphonates, to control scalesother than silica, corrosion inhibitors, biocides, dispersants,defoamers and the like. Accordingly, the present invention should beconstrued as broadly as possible.

As an illustration, below there are provided non-restrictive examples ofan aqueous water system that has been treated with methods conforming tothe present invention.

Examples of Silicate Scale Inhibitor Method

The following analytical tests were performed on a cooling tower systemtreated with the methods of the present invention to demonstrate theefficacy of the present invention for controlling the solubility ofsilica and silicate species, and preventing scale deposition of thesespecies. Two samples of each of the following: 1) varying source water;2) the resultant treated system water; and 3) tower sump insolubleaccumulations, for a total of six samples were analyzed from differentoperating time frames.

Although the exact mechanism of action of the process is not completelyunderstood, the methods of the present invention minimize the turbidityof the treated water, which is considered a demonstration of aneffective silica and silicate scale inhibitor. Methods that producetreated water of less than eight nephelometric turbidity units (NTU) areconsidered improvements over the current available technology. Turbiditymeasurements (Table 1) performed on samples taken from the coolingsystems, before and after filtration through a 0.45-micron filter,illustrate effective silicate inhibition in the treated water. Theturbidity levels are well below typical cooling tower systems, inparticular at such high concentrations (80 COC), and indicate themethods of the present invention provide controlled non-adherentprecipitation of excess silica and other insoluble materials enteringthe system. Clean heat exchanger surfaces have confirmed that the methodsilica precipitation is non-adherent. The precipitated silica forms arecontained in the cooling tower sump. However, the volume of precipitantand scrubbed accumulations in the tower sump were not appreciablygreater than previous treatment methods due to reduction of insolublemultivalent metal salt precipitates by pretreatment removal. TABLE 1Tower Water Turbidity Analyses Sample No. 1: (Turbidity, NTU) Neat, 4NTU; Filtered, 2 NTU Sample No. 2: (Turbidity, NTU) Neat, 3 NTU

The cooling tower and makeup water analytical tests performed in Table 2and Table 3 illustrate the effectiveness of the methods of the presentinvention in maintaining higher levels of soluble silica in the coolingtower system when parameters are controlled within the specified pH andlow makeup hardness ranges. Soluble silica residuals are present at 306and 382 mg/L in these tower samples at the respective 9.6 and 10.0 pHlevels. The lower cycles of concentration (COC) for silica in thesetower samples, as compared to the higher cycled residuals for solublechemistries (chloride, alkalinity, conductivity), indicate that excesssilica is precipitating as non-adherent material, and accumulating inthe tower basin. This is confirmed by the increased ratio of silicaforms found in tower basin deposit analyses. System metal and heatexchange surfaces were free of silica or other scale deposits. TABLE 2Cooling Tower Sample No. 1/Makeup/Residual Ratios (COC) SAMPLE/TESTSTower (*adjunct) Makeup (soft) COC Conductivity, 33,950 412 82.4 μmhos(Un-neutralized) pH 10.01 8.23 NA Turbidity, NTUs 3 0.08 NA NeatFiltered (0.45μ) — — — Copper, mg/L Cu ND ND NA Zinc, mg/L ND ND NASilica, mg/L SiO₂ 382 9.5 40.2 Calcium, mg/L 16.0 0.20 NA CaCO₃Magnesium, mg/L 3.33 0.05 NA CaCO₃ Iron, mg/L Fe ND ND NA Aluminum, mg/LND ND NA Al Phosphate, mg/L ND ND NA PO₄ Chloride, mg/L 6040 80 75.5Tot. Alkalinity, 13200 156 84.6 mg/LND = Not Detectable;NA = Not Applicable;COC = Cycles of Concentration

TABLE 3 Cooling Tower Sample No. 2/Makeup/Residual Ratios (COC)SAMPLE/TESTS Tower (no adjunct) Makeup (soft) COC Conductivity, 66,700829 80 μmhos (Un-neutralized) pH 9.61 7.5 NA Turbidity, NTUs 4 0.08 NANeat Filtered (0.45μ) 2 — — Zinc, mg/L ND ND NA Silica, mg/L SiO₂ 306.411 28 Calcium, mg/L 21.5 0.20 NA CaCO₃ Magnesium, mg/L 0.65 0.05 NACaCO₃ Iron, mg/L Fe ND ND NA Aluminum, mg/L ND ND NA Al Phosphate, mg/LND ND NA PO₄ND = Not Detectable;NA = Not Applicable;COC = Cycles of Concentration

Microscopic and chemical analysis of deposit samples from accumulatedresidue in the tower basin of a system treated by present methodologyare shown in Exhibit 1 and Exhibit 2. Both analyses illustrate thesignificant ratio of silica materials in the deposit. The majorproportion of this silica is the probable result of silica adsorption orreaction with insoluble precipitates of multivalent metals as theyconcentrated in the tower water. Visual inspections of heat transferequipment in the system treated by this method have confirmed that ithas remained free of silica and other scale deposits. System heattransfer efficiencies were also maintained at minimum fouling factorlevels.

Exhibit 1 MICROSCOPICAL ANALYSIS - POLARIZED LIGHT MICROSCOPY DEPOSITDESIGNATION: Cooling Tower Basin Deposit % ESTIMATED CONSTITUENTS >30Amorphous silica, including assorted diatoms, probably includingamorphous magnesium silicate; calcium carbonate (calcite) 1-2 Assortedclay material including feldspar; hydrated iron oxide; carbonaceousmaterial  <1 Silicon dioxide (quartz); assorted plant fibers;unidentified material including possibly aluminum oxide (corundum)

CHEMICAL ANALYSIS - DRIED SAMPLE DEPOSIT DESIGNATION: Cooling TowerBasin Deposit % ESTIMATED CONSTITUENTS 12.1 CaO 8.5 MgO 5.2 Fe₃O₄ 3.7Fe₂O₃ <0.5 Al₂O₃ 13.2 Carbonate, CO₂ 51.1 SiO₂ 5.7 Loss on IgnitionMost probable combinations: Silica ˜54%, Calcium Carbonate ˜32%, Oxidesof Iron ˜9%, Mg and Al Oxides ˜5%.Examples of Corrosion Inhibition Methods of the Present Invention

The data in Table 4 illustrate the effectiveness of the methods of thepresent invention in inhibiting corrosion for carbon steel and coppermetals evaluated by weight loss coupons in the system. No pitting wasobserved on coupon surfaces. Equipment inspections and exchanger tubesurface testing have confirmed excellent corrosion protection.Comparable corrosion rates for carbon steel in this water quality withexisting methods of the present inventions are optimally in the range of2 to 5 mpy. TABLE 4 CORROSION TEST DATA Specimen Type Carbon SteelCopper Test location Tower Loop Tower loop Exposure period 62 Days 62Days Corrosion Rate (mpy) 0.3 <0.1Examples of Scale Deposit Removal

The data in Table 5 illustrate harness (CaCO₃) scale removal from metalsurfaces in a tower system treated with the methods of the presentinvention through coupon weight loss reduction. Standard metal couponsthat were scaled with CaCO₃ film were weighed before and after ten daysof exposure and the visible removal of most of the scale thickness. Thedemonstrated CaCO₃ weight loss rate will provide gradual removal ofhardness scale deposits that have occurred in a system prior to methodtreatment. TABLE 5 SCALE DEPOSIT REMOVAL TEST DATA Specimen Type CarbonSteel Copper Test location Tower Loop Tower loop Exposure period 10 Days10 Days Scale Removal (mpy) 8.3 8.1

1. A method for controlling silica or silicate scale formation in anaqueous water system with silica contributed by source water, themethods of the present invention comprising the steps: a) removinghardness ions from said source water; b) controlling the conductivity ofsaid aqueous system water such that said aqueous system water possessesa conductivity from approximately 10,000 to 150,000 μmhos; and c)elevating and maintaining the pH of said aqueous system water such thatsaid aqueous system water possesses a pH of approximately 9.0 orgreater.
 2. The method of claim 1 wherein in step a), said hardness ionscomprise ions of calcium and magnesium.
 3. The method of claim 1 whereinsaid aqueous system water contains soluble SiO₂ in excess of 200 mg/L.4. The method of claim 3 wherein said aqueous system water containssoluble SiO₂ in excess of 300 mg/L.
 5. The methods of the presentinvention of claim 3 wherein in step a), said hardness ions are removedin amounts equal to or less than approximately 20% of the SiO₂ presentwithin said source water.
 6. The methods of the present invention ofclaim 3 wherein in step a), said hardness ions are removed in amountsequal to or less than approximately 5% of the SiO₂ present within saidsource water.
 7. The method of claim 1 wherein in step c), said pH ismaintained at 9.6 or higher.
 8. The method of claim 1 wherein in stepa), said hardness ions are removed via a method selected from the groupconsisting of ion exchange, selective ion removal with reverse osmosis,reverse osmosis, electro chemical removal, chemical precipitation,evaporation and distillation.
 9. The method of claim 1 wherein in stepc), said pH is increased by adding an alkali agent.
 10. The method ofclaim 8 wherein said alkali agent comprises sodium hydroxide.
 11. Themethod of claim 1 wherein in step c), said pH is elevated by evaporatinga portion of said aqueous system water.
 12. The method of claim 1wherein in step c), said pH is elevated by distilling a portion of saidaqueous system water.
 13. The method of claim 1 wherein in step c), saidsource water comprises water utilized for cooling processes, waterutilized for cooling tower systems, water utilized for evaporativecooling, water utilized for cooling lakes or ponds, water utilized forenclosed or secondary cooling and heating loops.
 14. A method forinhibiting corrosion of a metallic substance in an aqueous systemwherein said aqueous system derives water from make-up source water, themethods of the present invention comprising the steps: a) removinghardness ions from said source water; b) controlling the conductivity ofsaid aqueous system water such that said aqueous system water possessesa conductivity from approximately 10,000 to 150,000 μmhos; and c)elevating and maintaining the pH of said aqueous system water such thatsaid aqueous system water possesses a pH of approximately 9.0 orgreater.
 15. The method of claim 14 wherein in step a), said hardnessions comprise ions of calcium and magnesium.
 16. The method of claim 14wherein said aqueous system water contains soluble SiO₂ in excess of 200mg/L.
 17. The method of claim 14 wherein said aqueous system watercontains soluble SiO₂ in excess of 300 mg/L.
 18. The method of claim 14wherein in step a), said hardness ions are removed in amounts equal toor less than approximately 20% of the SiO₂ present within said sourcewater.
 19. The method of claim 16 wherein in step a), said hardness ionsare removed in amounts equal to or less than approximately 5% of theSiO₂ present within said source water.
 20. The method of claim 14wherein in step c), said pH is maintained at 9.6 or higher.
 21. Themethod of claim 14 wherein in step a), said hardness ions are removedvia a method selected from the group consisting of ion exchange,selective ion removal with reverse osmosis, reverse osmosis, electrochemical removal, chemical precipitation, evaporation and distillation.22. The method of claim 14 wherein in step c), said pH is increased byadding an alkali agent.
 23. The method of claim 22 wherein said alkaliagent comprises sodium hydroxide.
 24. The method of claim 14 wherein instep c), said pH is elevated by evaporating a portion of said aqueoussystem water.
 25. The method of claim 14 wherein in step c), said pH iselevated by distilling a portion of said aqueous system water.
 26. Themethod of claim 14 wherein said metallic substrate is selected from thegroup consisting of carbon steel, copper, copper alloy and stainlesssteel alloy.
 27. The method of claim 1 wherein prior to step a), saidmethods of the present invention comprises the step: a) analyzing saidsource water to determine the concentration of SiO₂ present therein. 28.The method of claim 14 wherein prior to step a), said methods of thepresent invention comprises the step: a) analyzing said source water todetermine the concentration of SiO₂ present therein.
 29. The method ofclaim 1 wherein in step b), said conductivity of said aqueous systemwater is controlled such that said aqueous system water possesses aconductivity from approximately 20,000 to 150,000 μmhos.
 30. The methodof claim 14 wherein in step b), said conductivity of said aqueous systemwater is controlled such that said aqueous system water possesses aconductivity from approximately 20,000 to 150,000 μmhos.
 31. The methodof claim 1, wherein said source water contains silica in an amount of4000 mg/L or less.